Nowadays, the IP Multimedia Subsystem (hereinafter IMS) enables network operators to offer their subscribers multimedia services based on, and built upon, Internet applications, services and protocols. The IMS architecture offers the opportunity to deploy peer-to-peer applications where two or more users directly exchange user data upon a session establishment via IMS. In this respect, different IMS services and applications as defined by 3GPP and OMA standards can be offered on top of the IMS. Some exemplary peer-to-peer applications may be Multimedia Telephony, Push to Talk over Cellular, streaming, real-time video sharing, file sharing, and gaming.
On the other hand, and in order to provide a satisfactory and reliable service experience, network operators need to take a special care of the quality of service (hereinafter QoS), effective charging and potential fraud on the usage of services. To this end, 3GPP standards provide for a so-called Policy and Charging Control (hereinafter PCC) architecture to help network operators to control the above issues. The PCC architecture basically consists of an Application Function (hereinafter AF) offering applications requiring a dynamic policy and/or charging control of traffic plane resources, a Policy and Charging Enforcement Function (hereinafter PCEF) providing control over the user plane traffic and its QoS, and a Policy and Charging Rules Function (hereinafter PCRF) responsible for installing required PCC rules at the PCEF to ensure that only authorized media flows associated to requested services are allowed and are applied, for example, the right bandwidth, charging and priority.
In accordance with 3GPP standards, communications between IMS subscribers and IMS entities, as well as between IMS entities themselves, are carried out with a so-called Session Initiation Protocol (hereinafter SIP) for signalling multimedia sessions, and with a Session Description Protocol (hereinafter SDP) for exchanging information about media flows associated with the multimedia sessions. More specifically, transport connections may be dynamically negotiated with help of the above SIP and SDP protocols between two end-points, or between two IMS peer-to-peer applications. In this respect, 3GPP TS 23.203 proposes the above PCC architecture to effectively support the IMS peer-to-peer applications with a first mechanism to selectively control IP flows associated with IMS sessions of a subscriber, and a second mechanism to selectively determine the bearer usage of dynamically negotiated IP flows in order to apply an effective policy and charging for each service.
A complete solution for the support of IMS services and applications includes user equipments (hereinafter UE), IP-Connectivity Access Networks (hereinafter IP-CAN), and specific functional elements of the IMS, namely IMS entities as described in 3GPP TS 23.228 “IP Multimedia Subsystem (IMS); Stage 2”. An exemplary IP-Connectivity Access Network is the GPRS core network with GERAN and/or UTRAN radio access networks.
A traditional scenario may be where IMS services and applications are offered over a GPRS connection, that is, where GPRS is the IP-CAN. In this scenario, a Proxy Call Session Control Function (hereinafter P-CSCF) server acting as entry node in the IMS architecture may include the AF functionality and is located in the signalling plane; a Gateway GPRS Support Node (hereinafter GGSN) may include the PCEF functionality and is located in the bearer plane; whereas the PCRF may sit between the signalling plane and the bearer plane, thus being connected with the P-CSCF and the GGSN.
In a conventional IMS network, multiple factors may make the P-CSCF behave in a different way. For example, the P-CSCF might have to decide: payload types to be accepted, maximum number of media components to be accepted per media type, codecs supported, bandwidth permitted per media type, etc; and these decisions can be taken in the P-CSCF based on information received from a UE. This situation may lead to inconsistencies in the case of a split UE, for example, where a mobile phone connects a Personal Computer with an IP-CAN, since a consistent UE behaviour cannot be guaranteed at the time of initiating the establishment of SIP sessions. In this scenario, a conventional P-CSCF is statically configured in accordance with preferences of the owning network operator and regardless specific conditions that could appear. A P-CSCF thus statically configured always behaves in the same way, regardless specific conditions that could appear.
In addition, where PCC comes into place, more data have to be configured in the P-CSCF in order to estipulate interactions with the PCC architecture during the SIP session establishment and how to progress it, what information shall be provided to the PCC architecture, and what information shall be received from the PCC architecture, amongst others. As in the above case where a PCC architecture is not connected with the IMS, all these behaviours can be statically configured in the P-CSCF so that no specific condition can be distinguished from an operational point of view.
Moreover, currently existing networks are evolving towards so-called fixed-mobile-convergence networks, where the user can make use of IMS services from different accesses with different technologies. Besides, network operators promote different user categories, with different tariffs and available services. In order to cope with all these requirements, the IMS network needs to be adapted to work in the most optimal way for every user and at every access.
Static configurations for handling IMS sessions imply strong limitations to the above network scenarios where there is no user differentiation, and where IMS sessions always proceed in the same way regardless user categories and regardless whether a user has accessed through a fixed or a mobile network.